[Feature Request] Add effort level to statusline JSON input and session state exposure

Question

**Bug Description**
Unable to show "max" effort level since it is session-only.

effortLevel be added to the statusline JSON input.
There's no supported way to access the **session-only effort level** from the statusline. It's not in the JSON input, not written to any settings file, and there's no env var or temp file exposing it.

The statusline already exposes other session state (model, context usage, cost, etc.). Effort level is a natural addition.

**Environment Info**
- Platform: darwin